Keyboard: Bpiphany Frosty Flake Refactor, Configurator support and readme cleanup (#4648)
* Frosty Flake: layout macro refactor
- frosty_flake.h updated to use #pragma once
- KEYMAP renamed to LAYOUT
- KEYMAP_TKL renamed to LAYOUT_tkl
* Frosty Flake: keymap refactor
- config.h files updated to #pragma once
- deleted deprecated build script rules from rules.mk
- keymap.c files:
- #include QMK_KEYBOARD_H
- updated layout macro name
- white space changes for readability
* Frosty Flake: Configurator support
* Frosty Flake: readme cleanup
- Fixed Hardware Availability link (old link was 404)
- tiny grammar fix (colon missing on compile-and-flash instructions)
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